Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $142.64   12.668%   $160.7096   $160.71   $160.70   $160.70  
  Purchase #2 $173.66   13.563%   $197.2135   $197.21   $197.20   $197.20  
  Purchase #3 $208.90   7.812%   $225.2193   $225.22   $225.20   $225.20  
  Purchase #4 $236.74   13.619%   $268.9816   $268.98   $269.00   $269.00  
  Purchase #5 $60.39   4.562%   $63.145   $63.15   $63.15   $63.10  
  Purchase #6 $31.76   10.696%   $35.157   $35.16   $35.15   $35.20  
  Purchase #7 $91.51   3.235%   $94.4703   $94.47   $94.45   $94.50  
  7 purchase totals = $945.60       $1,044.8963   $1,044.90   $1,044.85   $1,044.90